Abstract

Understanding the patterns and ecological determinants of β diversity in freshwater ecosystems is fundamental to biogeography, conservation biology, and environmental management. It has been proposed that β diversity can be divided into contributions of individual sites (LCBD) or species (SCBD) to total β diversity. However, the patterns and underlying mechanisms of LCBD and SCBD remain understudied in freshwater fish. Here, using fish assemblages sampled from the Chishui River basin, we analysed β diversity based on both abundance and presence-absence data. We also examined the relationships between LCBD and SCBD with site (i.e., community abundance, species richness, functional diversity indices, environmental factors, and spatial variables) and species (i.e., occupancy, total abundance, niche position and breadth, and functional traits) characteristics, respectively. Our results revealed that fish LCBD in the Chishui River basin was well explained by both environmental and spatial factors. Fish LCBD was negatively related to species richness and community abundance, showing that sites with high ecological uniqueness generally supported low fish richness and abundance. Furthermore, functional features of fish assemblages were also significantly associated with LCBD, with high LCBD associated with high functional specialization, originality, and uniqueness, but low functional richness, divergence, and dispersion. Abundance-based SCBD showed positive relationships with both occupancy and total abundance, whereas there were hump-shaped relationships between presence-absence SCBD and occupancy and total abundance. Niche position was negatively correlated with SCBD, whereas niche breadth and functional traits were not significant correlates of SCBD. Overall, this study suggests that understanding contributions of sites and species to β diversity is key to understanding biodiversity variation and its applied repercussions. Our results advocate the importance of environmental conditions and between-site connectivity for effective conservation of riverine fish diversity. Moreover, a simultaneous application of LCBD, species richness, SCBD, and rare species would be the most suitable approach for biodiversity conservation.